Courses/Computer Science/CPSC 203/CPSC 203 2007Summer L60/CPSC 203 2007Summer L60 Lectures/Lecture 7

Lecture 7

• Query Language
• How to produce a query
• Text Readings: Chapter 9 "Circuits" pp 386-393

Glossary

• SQL (Structured Query Language)Terms

has five key terms in any SQL statement

• • Select (Which Columns)
  • From (Which Tables)
  • Where (Which Rows)
  • Group By (Which Group Fields)
  • Having (Which Groups)
• Terms of Boolean Logic
  • And
  • OR
  • NOT
  • XOR
• Boolean Logic
• Circuit

The terms of Boolean Logic were illustrated by their respective Truth Tables. See also Wikipedia: http://en.wikipedia.org/wiki/Truth_table (note that in class we used 1 where they use "T", and we used 0 where they use "F"). Truth table values were then related to Logic gates: http://en.wikipedia.org/wiki/Logic_gates. Finally, logic gates were combined to build more complex circuit diagrams : http://en.wikipedia.org/wiki/Logic_gates.

For more on Boolean Logic please see: http://en.wikipedia.org/wiki/Boolean_Logic

Queries

Trace (Query Evaluation)Steps

Basic:

1. Cross product from tables in 'FROM' (like the Union set)
2. Remove rows when 'WHERE' is false
3. Return true rows according to 'SELECT'

Summarize Data:

1. Arrange rows by 'GROUP BY'
2. Remove rows where 'HAVING' is False
3. 1 Row for each true group according to 'SELECT'

Examples of the Trace mechanism were illustrated through a series of increasingly complex queries beginning with all data in a single table, to queries asking for summary data across several tables.

Resources

For database resources see Lecture 4

The primary resource for this lecture was:

• Onest Zeros -- Understanding Boolean Algebra, Digital Circuits and the Logic of Sets. 1998. By John R. Gregg

Supplementary References are:

• Logic. A Very Short Introduction. 2000. By Graham Priest.
• Logic Made Easy. How to Know When Language Decieves You. 2004. By Deborah J. Bennett.
• Feynman Lectures on Computation. 1996. By Richard P. Feynman.